1. Field of the Invention
The present invention relates to papermakers fabric. More particularly, the present invention relates to the weave construction of forming fabrics and press felts.
2. Description of the Prior Art
Papermaking machines transform an aqueous slurry of pulp fibers into a continuous paper sheet. The papermaking process starts in a forming section of the papermaking machine where an aqueous pulp slurry is deposited onto forming fabrics having desired characteristics for retaining the pulp fibers while allowing water to pass through the fabric. In the forming section, the pulp fibers are formed into an aqueous paper web. The paper web is then transferred to and carried by press felts through a press section of the papermaking machine where additional water is removed by conveying the paper web through one or more press nips. The paper web is then transferred to and carried through a drying section on dryer fabrics to remove additional water through forced evaporation. The designs of papermakers fabrics used on each section of the papermaking machine vary in accordance with function.
Forming fabrics may possess fine mesh weave to support the paper fibers in the slurry. Additionally, a fine weave avoids paper markings on the forming paper. Forming fabrics should also possess good drainage characteristics to facilitate paper formation during the initial water removal from the slurry. Furthermore, forming fabrics should withstand tensile loads in the machine direction and compressive buckling loads in the cross machine direction.
For press felts, several other characteristics are desired. Press felts should maintain sufficient void volume to allow the efficient transfer of water out of the aqueous paper web as it is conveyed through press nips. The press felts should be designed to withstand the humidity and temperature rigors of the press section. Furthermore, the felts should maintain uniformity over a substantial time period as they are used on the press section. In light of these conditions and factors, it is desired to provide press felts with enhanced stability, low flow resistance, compaction resistance, increased void volume, increased cleanability, and durable pressing uniformity.
Attempts have been made to overcome the problems associated with forming fabrics and press felts. For example, U.S. Pat. Nos. 4,333,502 and 4,171,009 (Karm) disclose a two layer forming fabric with a distinctive weave and sequence pattern. Although a two layer forming fabric is disclosed, both patents teach a weave pattern in the machine direction and do not exhibit the same level of support surface as the instant invention. U.S. Pat. No. 4,414,263 (Miller et al.) discloses a two layer press felt based fabric having stacked MD yarns with a simple two layer weave. U.S. Pat. Nos. 5,449,026; 5,167,261; and 5,103,874 (Lee) disclose various weaves for fabrics having flat stacked MD yarns.
Additionally, U.S. Pat. Nos. 4,461,803 and 4,537,816 (Booth et al.) disclose press base fabrics having stacked MD yarns woven with CMD yarns which float over multiple MD yarns, but do not carry extensive floats along the paper sheet support surface.
While these patents disclose fabrics which perform satisfactorily in many applications, it is desirable to provide a structure for forming fabrics and press felts, having characteristics which more particularly solve the problems associated with papermaking fabrics and processes as previously discussed.